This project consists of two related parts, which taken together, form the cornerstone for the achievement of a longer range goal. In the first part of the project, the plan to develop a quantitative description of the heart as a pump under in vivo conditions and taking into account its time-varying properties will be continued. In the second part, a range of animal experiments will be pursued for the purpose of arriving at a definitive interpretation of the physical phenomena observed in arteries. These experiments are supported by appropriate bench experiments currently in a well advanced state of development. These two parts will provide the basis for the analysis of the interaction between the ventricle and the arteries, the long range goal of this project.